Modern Vespa

1. Now the the bike is up and running....sweetly I might add....after my tinkering, I have been for three or four 5 mile rides, and twice my plug HT lead has loosened to the point that the bike has lost power. I don't know if its that the pinasco 102cc head puts the plug in a slightly different position, but the rubber plug shroud does not engage with the head shroud. I just tightened the lead from plug to the first retaining clip to see if that helps but appreciate any input.

2. I decided to check the plug after the last run, for an informal plug chop. The color looks good, light coffee brown, but I was surprised that the plug is a BR5HS,which is fairly hot isn't it? Based on me having the 102cc pinasco kit and 16/16 carb with 74 main and 42 idle, what is the significance of that plug?....bearing in mind my runs are all about 5 miles with minimal WOT

Yes, I reckon the Pinasco 102cc head is putting the plug in a slightly different position. Try a different plug cap sans shroud. (ignore any subsequent comments that "without the shroud you'll upset the uber critical flow of cooling air and the engine will self destruct").

If the color looks good, light coffee brown, I'd say it 's pretty well dialled in. A BR5HS is probably fine for puttin' around but as you say would be a little hot for any hard work. Put a 6, 7 or even 8 in it and leave the 5 in the tool box as a spare.

Get rid of the resistor plug and put in a b8

if you have enough of a HT lead length to the plug cap you can cut off about a 1/2 inch from it and then reattach the plug cap... that might help tighten things up. If that cap is the type where you have to remove the top "hat" off the spark plug then that should be addressed asap. The cap below is a nice upgrade.

if the cap is loose and spark get erratic the plug would look richer than it really is since some mixture is not being burned when it should be.

these are nice and last a long time

I just renewed all the caps on all my bikes. exactly like those again ^^^ the rubber cap at the end is nice.

yes, the plug does not have the hat....what is the significance of the hat?

Look like I have some more tinkering to do

I would have thought an 8 was going too far?...6 or 7 seem standard

if you have to remove that top part of the spark plug to make it fit then your exposing the threads. These threads wear down the plug cap contact surface after you take it on and off a few dozen times (plug chops). Then you get erratic sparking. Happened to me. I only buy the above plug caps.

#7 for in town
#8 for longer rides
some people rock #9 spark plugs

most stock vespas came with #6 and that is what the manuals all say but that is old info and not the best for todays fuels.